1. Field of the Invention
The present invention relates to industrial manufacturing of an assembly formed by a sheet of glass and a sealing strip of a polymeric material surrounding the rim thereof, particularly a plant for the preparation of the rim of sheets of glass so as to make them suitable to be treated in a successive operation of assembling the polymeric strip.
2. Description of the Prior Art
From the prior art, assemblies formed by a sheet of glass and a polymeric sealing strip surrounding the rim thereof are well known. Hereinafter they will be indicated by the term "capsulated products". The capsulated products which are particularly used in the field of automobile glazing, have the advantage of being suitable to be mounted at very low cost on the motor vehicle bodies.
In U.S. Pat. No. 4,561,625 a process is described for automatically assembling a sealing strip on the rim of a sheet of glass, consisting in polymerising directly on the glass rim the polymeric material forming the sealing strip, as injected onto said rim at a controlled pressure and temperature.
In U.S. Pat. No. 4,561,625 filed Dec. 23, 1983, an apparatus, particularly a mold, is described for the formation, by means of injection and polymerisation of polymeric material, of a sealing strip which capsulates the peripheral edge portion of a sheet of glass, for example a motor vehicle windscreen, in such a manner that the glass and sealing strip assembly so obtained can be directly mounted onto the body of the vehicle.
The manufacturing of the glass and sealing strip assemblies as previously described, is effected in a work cycle formed by three main operations: a treating operation for preparing the rim of the sheet of glass, a capsulating operation and a finishing operation of the product.
Each of the three main operations in turn consist of a certain number of elementary steps.
The treating operation provides a preparation of the upper face of the glass rim in order that it can be intimately bound to the polymeric sealing strip which is applied in the capsulating operation. By the term "upper face" of the sheet, the face which remains on the exterior of the car when the glass is mounted is intended.
For this purpose the rim of ths sheet has first to be accurately cleaned and it then has to be coated with a chemical composition having the function of promoting the glass-sealing strip bond and which is currently denominated adhesion promoter.
The purpose of the finishing operation is to provide the capsulated product with all the aesthetic characteristics for commercial requirements.
Of the aesthetic characteristics which are provided in the finishing operation, one of the most important is the resistence of the sealing strip to U.V. radiation. In fact it is known that the polyurethane strip has the tendency to be opacified on its surface, thus loosing its brightness after prolonged exposure to U.V. rays. To overcome said drawback, the prior art teaches that it is sufficient to cover the polyurethane with a paint which is opaque to the U.V. radiation.
Rather than spraying the capsulated product in the finishing operation, painting can also be carried out along with the capsulating operation by coating a suitable paint onto the surface of the mould.
In both cases an undesirable blotting of the surface not to be involved in the capsulation can occur. In fact spraying could lead to an inaccurate application of the paint, and coating the mould could lead to a localised seepage of the paint towards the inner surface of the glass.
As in the application of the adhesion promoter and paint a protection of the sheet surface not to be involved in the capsulation is necessary, the prior art afforded this protection by masks of a sufficiently light and resistant material applied by hand during the operations and so shaped as to conform to the surface to be protected.
This produces the following disadvantages: a need to prepare a mask for each model of glass to be capsulated; an excessive man-power during the course of working with frequent handling of the glass which could cause damage, such as scratches and chipping.